PET^OELLT— rOSSELS OF DETOT!?' AIJJ) COr^NWALL, 



15 



' Catalogue,' the Heteropodous Mollusca are, in Table I., included in 

 the class Gasteropoda. 



It is scarcely necessary to remark that the fossils of Devon and 

 Cornwall do not fully represent the organisms of the Devonian age, 

 as seven other classes — Pisces, Pteropoda, Cirrepedia, and Annelida, 

 amongst animals, and Cellulares, Monocotyledones, and Polycotyle- 

 dones amongst plants — have been found in rocks of this age else- 

 where ; and of these the two first and the fifth have been met with 

 in other British localities. The reptiles Sieganolepis and Telerpeton, 

 of the Elgin Sandstone, are not enumerated here, as some doubt 

 attaches to the question of their chronology, if indeed they are not 

 certainly Triassic. The single articulated class, Crustacea, is by no 

 means rich in any way ; with one exception, all its genera are Tri- 

 lobites, and commonly contain but one species each. The most 

 important class numerically is Brachiopoda, to which one hundred 

 and eight species belong, tliat is, thirty-one per cent, of the entire 

 series. The families and genera of Cephalopoda are richer in species 

 than those of any other class, averaging sixteen for each family, and 

 ten for each genus. 



The most striking fact in this connection is the specific abundance 

 of Brachiopoda and Cephalopoda, and the paucity of the classes 

 Lamellibranchiata and Gasteropoda, as compai'ed with the numerical 

 rank of the same classes in the existing Fauna. This fact will, 

 perhaps, be most strikingly exhibited by the following table, which 

 has been thus computed: in the left-hand column the aggregate 

 number of the species of fossil mollusca found in Devon and Corn- 

 wall has been put = one thousand, and the numbers belonging to 

 each class computed to this ; the right-hand column has been formed 

 on the same principle, and is based on the data given by Forbes and 

 Hanley in their ' History of British Mollusca.' 



TABLE II. 





Devonian Mollusca of 







Devon and 



Existing British 





Cornwall. 



Mollusca. 





42 



72 





410-5 



15-5 





186 



359-5 





179 



521-5 





182-5 



31-5 





1,000 



1,000 



It appears, then, that within existing British seas the Lamelli- 

 branehiates are about twenty-four times more numerous specifically, 

 than the Brachiopods, whilst within, what may be called, the same 

 area, the latter were to the former, during the Devonian period, 



